1. Technical Field
This invention relates generally to an apparatus and method for holding workpieces during inspection or dimensional checking.
2. Discussion
In the manufacturing environment, parts are manufactured to strict specifications. For quality control purposes, these parts are checked on a scheduled basis against a master part or a set of specifications. With the constant demand for continual improvement in the manufacturing processes and cost reduction, design tolerances and cost budgets are becoming more stringent. Dimensional control checks are normally performed on the parts using jig and fixture arrangements that support the parts in predetermined locations. Once the part is secured in this predetermined location, dimension checking can be achieved by a manual process, such as plug gages or datamytes or automated systems, like CMM machines. In either case, it is critical that the parts can be repeatedly placed in the same location.
In the past, specific holding devices were often constructed for each part. An array of fixed stanchions would be mounted to a base that would support a part. This method is very costly since the fixture can typically be used for only one part. The fixtures are large and bulky creating a serious storage problem.
Similarly, the parts have a limited life. When a major change is made to the part or the part is deleted, the fixture becomes obsolete. To try and reduce this waste, several inventions have been purposed to use the same base and supporting means, reducing the amount of waste when a part becomes obsolete.
U.S. Pat. No. 5,026,033 to Roxy discloses this type of adjustable alignment positioners using a master base template. A series of threaded holes are used and single point attachments are inserted to support the piece. Although this system is effective, lengthy setup times are required. Locations of the attachments must be predetermined and the repeatability of the fixture must be checked and verified.
U.S. Pat. No. 4,968,012 to Haddad et al. discloses a modular workpiece having precisely drilled counter-bored holes forming a matrix for attaching stanchions thereto. The holes alternate in diameter between a larger diameter and a smaller diameter and use a combination of a round and diamond shape attaching means with precision bushings therein. This system is very costly due to the precision required when drilling the matrix in each face of the cube, the bushings, and manufacturing the pin assembly. Additionally, the tolerance stack-up inherent in this system adds an additional burden when manufacturing.
This invention eliminates one or more of the above-described problems as well as provides a workpiece holding apparatus which is easier to manufacture, allows for quick setup, provides universal support means, and affords positive and repeatable location of a plurality of parts.